Session Handling Changes between 4.2.3 and 4.3.1

Hi, i worked for a while with the Windows Version of PHP 4.1 and later 4.2. After I changed my Development Environment to Linux and the PHP Version 4.3.1, some or all of my formerly projects showed some errors or are just working in a different way than before, due to the changes in session handling. I have read thru the session handling parts of the 4.2.3 Docs for PHP and compared it to the way i have programmed the session handling in my websites. I could not really find any differences. I do start the sessions in an global.inc.php file with session_start() and after that i register them for exam- ple with session_register('user') for Customermanagement. After that I'm referencing the session thru $_SESSION['user']['username'] and so on. I have written one administration tool where everything works pretty fine this way, but on two other webpages where the usermanagement does not really work this way. In php.ini there is written some about an 4.2.3 Error which lets me initialize sessions in a wrong way, but in 4.3 this error should not occure anymore. Do i use the sessionmanagement in the right way, or do i do something wrong. When i use a windows PC for the development everything works fine, just Linux seems to be a little more konservative. It would be nice, to get an explaination and maybe so- lution for this strange problem. Thanks indeed Sascha